Flexible bone implant

ABSTRACT

Examples of devices and methods for stabilizing a fracture in a bone include a body having an elongate distal portion having an outer surface defining a screw thread and an elongate proximal portion having a non-threaded outer surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 15/285,608, filed Oct. 5, 2016, which is a continuation-in-partof U.S. patent application Ser. No. 15/197,879, filed Jun. 30, 2016,which claims the benefit of U.S. Provisional Application No. 62/191,904,filed Jul. 13, 2015, and U.S. Provisional Application No. 62/238,780,filed Oct. 8, 2015, all of which are hereby incorporated by reference.

FIELD OF THE INVENTION

Examples of the invention relate generally to orthopedic devices for thesurgical treatment of bone and, more particularly, to the stabilizationof bones with an intramedullary device.

BACKGROUND

Orthopedic medicine provides a wide array of implants that can beattached to bone to repair fractures. External fixation involves theattachment of a device that protrudes out of the skin, and thereforecarries significant risk of infection. Many fractures in long bones canbe repaired through the use of bone plates, which are implanted andattached to lie directly on the bone surface. The bone plate thenremains in the body long enough to allow the fractured bone to healproperly. Unfortunately, such bone plates often require the surgicalexposure of substantially the entire length of bone to which the plateis to be attached. Such exposure typically results in a lengthy andpainful healing process, which must often be repeated when theimplantation site is again exposed to allow removal of the plate. Thereis a need in the art for implants and related instruments that do notrequire such broad exposure of the fractured bone, while minimizing theprobability of infection by avoiding elements that must protrude throughthe skin as the bone heals.

SUMMARY

Examples of the invention provide devices and methods for stabilizingfirst and second bone portions relative to one another.

In one example of the invention, a bone implant includes an elongatebody having a distal portion and a proximal portion spacedlongitudinally relative to a longitudinal axis. The distal portion has ahelical distal thread formed on it. The distal thread has a majordiameter, a minor diameter, and a pitch. The distal thread is operableto bend as it is threaded into a bone to follow a curved path. Thedistal thread has a bending stiffness and the proximal portion has abending stiffness. The bending stiffness of the proximal portion isgreater than the bending stiffness of the distal thread.

BRIEF DESCRIPTION OF THE DRAWINGS

Various examples of the invention will be discussed with reference tothe appended drawings. These drawings depict only illustrative examplesof the invention and are not to be considered limiting of its scope.

FIG. 1 is a side elevation view of a bone implant according to oneexample of the invention;

FIG. 2 is a detail view of the bone implant of FIG. 1;

FIG. 3 is a detail view of the bone implant of FIG. 1;

FIG. 4 is an end view of the bone implant of FIG. 1;

FIGS. 5-7 are side elevation views of a set of differently sized boneimplants like that of FIG. 1;

FIGS. 8-10 are partial sectional views showing the insertion of the boneimplant of FIG. 1 into bone;

FIGS. 11-35 illustrate a surgical procedure utilizing the bone implantof FIG. 1;

FIG. 36 is a perspective view of a bone implant according to one exampleof the invention;

FIG. 37 is a top plan view of the bone implant of FIG. 36;

FIG. 38 is a side elevation view of the bone implant of FIG. 36;

FIG. 39 is an end view of the bone implant of FIG. 36;

FIG. 40 is a sectional view taken along line 40-40 of FIG. 37;

FIG. 41 is an exploded sectional view taken along line 40-40 of FIG. 37;

FIG. 42 is a cross sectional view of a bone implant according to oneexample of the invention;

FIG. 43 is an exploded cross sectional view of the bone implant of FIG.42;

FIG. 44 is an exploded side view of a bone implant according to oneexample of the invention;

FIG. 45 is an assembled sectional view taken along line 45-45 of FIG.44;

FIG. 46 is an exploded side view of a bone implant according to oneexample of the invention;

FIG. 47 is an assembled sectional view taken along line 47-47 of FIG.46;

FIG. 48 is an end view of the bone implant of FIG. 46;

FIG. 49 is a cross sectional view taken along line 49-49 of FIG. 47;

FIG. 50 is a top view of a bone implant according to one example of theinvention;

FIG. 51 is an end view of the bone implant of FIG. 50;

FIG. 52 is a front view of the bone implant of FIG. 50;

FIG. 53 is a cross sectional view taken along line 53-53 of FIG. 52;

FIG. 54 is a perspective view of a surgical application of a boneimplant according to one example of the invention;

FIG. 55 is a perspective view of a surgical application of a boneimplant according to one example of the invention; and

FIG. 56 is a perspective view of a surgical application of a boneimplant according to one example of the invention.

DESCRIPTION OF THE ILLUSTRATIVE EXAMPLES

The term “transverse” is used herein to mean not parallel. FIGS. 1-4depict a bone implant 100 according to one example of the inventionhaving an elongate body 102 with a distal portion 104, a mid-portion 106and a proximal portion 108 spaced longitudinally relative to alongitudinal axis 110. The distal portion 104 includes a helical thread112 having a major diameter 114, a minor diameter 116, and a pitch 128.The mid-portion 106 has a non-threaded outer surface 118 with an outerdiameter 120. In the illustrative example of FIGS. 1-4, the mid-portionouter diameter 120 is equal to or greater than the thread major diameter114. The distal threaded portion 104 is operable to bend as it isthreaded into a bone to follow a curved path. For example, the bendingstiffness of the distal threaded portion 104 is such that it will bendto follow a curved path in human bone. Such a curved path may bedefined, for example, by a curved hole in the bone, a guide wire, or anatural bone feature such as a non-linear intramedullary canal boundedby cortical bone. This is distinct from prior art threaded implantswhich if started on a curved path in human bone would, when advanced,continue in a straight line and thus deviate from the curved path andform their own, straight, path through the bone. Preferably the bendingstiffness of the threaded distal portion 104 is lower than the bendingstiffness of the mid-portion 106. The relatively lower bending stiffnessof the threaded distal portion 104 causes the threaded distal portion tobend to follow a curved path while the relatively higher bendingstiffness of the mid-portion causes the mid-portion to remain straightto stabilize first and second bone portions relative to one another at abone interface such as at a fracture, osteotomy, or fusion site. Thedifference in bending stiffness between the threaded distal portion 104and the mid-portion 106 may be achieved in different ways. For example,the threaded distal portion 104 and the mid-portion 106 may be made ofdifferent materials and/or may have different sectional moduli. In theillustrative example of FIGS. 1-4, the threaded distal portion 104 andthe mid-portion 106 have different sectional moduli. The threaded distalportion minor diameter 116 is less than the outer diameter 120 of themid-portion 106 and the threaded distal portion major diameter is lessthan or equal to the outer diameter 120 of the mid-portion 106.Preferably, the ratio of the bending stiffness of the mid-portion 106 tothe bending stiffness of the threaded distal portion 104 is in the rangeof 1.5:1 to 100:1. More preferably, the ratio is in the range of 2:1 to20:1. For example, implants according to examples of the presentinvention and suitable for internal fixation of a clavicle fracture andthat fall within these ranges may have a major diameter 114 in the rangeof 4-6.5 mm, a minor diameter 116 in the range of 2.5-3.5 and acannulation 101 with a diameter in the range of 1-2 mm. Preferably, theimplant 100 is made of a polymer.

Table 1 compares the calculated load required to bend a cantileveredtube of 3 mm outside diameter and 1.5 mm inside diameter around a radiusof 50 mm and an arc length of 26 mm for different materials. Thetitanium and stainless steel alloys are predicted to have a requiredload approximately 10 times that of the PEEK and PLLA. These loads wouldbe greater than the bone could withstand and a threaded device made ofthose materials would not follow a curved path in the bone but wouldinstead cause the bone to fail. In the case of the highly cold workedstainless steel, even if the bone could withstand the load, the implantwould fail since the minimum bend radius before failure of the implantis greater than 50 mm.

TABLE 1 Load at 50 mm bend radius Yield Failure Yield Failure FlexuralStress Stress Strain Strain Modulus Load Material (MPa) (MPa) (%) (%)(MPa) (N) PEEK 100 115 2.5% 20% 4 9.8 ASTM F2026 PLLA 90 100 2.6% 25%3.5 8.7 Ti—6Al—4V 880 990 0.8% 14% 114 91.7 ELI ASTM F136 316LVM 14681696 0.7% 3% 197 Not Stainless Steel possible ASTM F899

Another way to quantify the bending stiffness of the threaded distalportion 104 is by the amount of torque required to turn the threadeddistal portion 104 into a curved bone hole having a specified radius ofcurvature. For example, the threaded distal portion 104 preferablyrequires a torque less than 20 in-lbs to turn the distal threadedportion 104 into a bone to follow a curved path having a radius ofcurvature of 50 mm. More preferably the required torque is less than 10in-lbs. More preferably the required torque is less than 5 in-lbs. Morepreferably the required torque is approximately 2 in-lbs.

Table 2 compares the measured torque required to advance a threaded tube25 mm into a 50 mm threaded radius formed in a rigid test block. Thetubes were all machined to the same geometry but of different materials.The thread major diameter was 4.25 mm, the minor diameter was 3.0 mm andthe inner diameter of the tube was 1.5 mm. A rigid block was preparedhaving a curved, threaded path. Such a path has a pitch that is wider onthe outside of the curve and a pitch that is narrower on the inside ofthe curve corresponding to the shape of the thread when it is curved.Multiple samples of each tube were inserted into the block over an arclength of 25 mm. The maximum torque for each revolution was measured andit was found that the torque increased for each revolution. In Table 2,the range is the range of torque values from the first to the lastrevolution. The average is the average of the torque values for allrevolutions. The peak is the highest torque value and in all casesoccurred in the last revolution. However, the torque values for eachmaterial were relatively constant over the last few revolutions. Thetitanium and stainless steel alloys had measured torque valuesapproximately 10 times that of the PEEK. These tests were conductedusing a threaded block made of tool steel with a strength greater thanthat of the materials being tested in order to compare the torquevalues. As pointed out relative to Table 1, the loads generated from themetal implants would be greater than the bone could withstand and athreaded device as described herein made of these metals would notfollow a curved path in the bone but would instead cause the bone tofail.

TABLE 2 Torque to thread around rigid 50 mm radius Range Average PeakMaterial (in-lbs) (in-lbs) (in-lbs) PEEK  0-2.0 1.4 2.0 ASTM F2026Ti—6Al—4V 0.7-25 16 25 ELI ASTM F136 316LVM 0.5-20 13 20 Stainless SteelASTM F899

In addition to bending stiffness advantages, having the threaded distalportion major diameter less than or equal to the outer diameter 120 ofthe mid-portion 106 allows the distal threaded portion 104 to passthrough a passage in a bone that will be a sliding or press fit with themid-portion 106. A bone implant so configured, as shown in theillustrative example of FIGS. 1-4, can have an intramedullary canalfilling mid-portion 106 providing solid support to a bone interface anda relatively bendable distal threaded portion 104 following a curvedpath such as for threading into a distal portion of a curved bone tosecure the implant in the bone.

The proximal portion 108 may be identical to the mid-portion 106.Alternatively, the proximal portion may have a positive driverengagement feature (not shown) such as internal or external non-circularsurfaces, profiles, or holes. For example, an internal or externalslotted, threaded, triangular, square, hexagonal, hexalobular, or otherdrive feature may be provided. In addition, as shown in the illustrativeexample of FIGS. 1-4, the proximal portion 108 may include an optionalexternal helical thread 122 able to engage a bone portion to provideproximal fixation of the implant. For example, the proximal thread 122may have a major diameter 124, a minor diameter 126, and a pitch 130. Inthe illustrative example of FIGS. 1-4, the mid-portion outer diameter120 is equal to the proximal thread minor diameter 126 and the distalthread major diameter 114. The proximal portion may alternatively, or inaddition, receive a locking member such as a pin or screw transverse tothe longitudinal axis to lock a proximal bone portion to the nail. Thelocking member may be drilled through the proximal portion. Preferably,the proximal portion has one or more transverse holes formed through itfor receiving the locking member.

The distal and proximal thread pitches 128, 130 may advantageously bethe same or different depending on the application. For example, tostabilize a fracture, the implant 100 may be inserted into a bone acrossthe fracture so that the distal thread 112 is engaged with bone distalto the fracture and the proximal thread 122 is engaged with boneproximal to the fracture. If the bone portions on either side of thefracture are reduced to a desired final position prior to inserting theimplant 100, then it is advantageous for the thread pitches 128, 130 tobe equal so that insertion of the implant does not change the relativepositions of the bone portions. If on the other hand, it is desirable tomove the bone portions relative to one another by the action ofinserting the implant then it is advantageous for the pitches 128, 130to be different. For example, to move the bone portions closer togetherto reduce the fracture, the distal thread pitch 128 may be made greaterthan the proximal thread pitch 130 so that with the distal thread 112engaged distally and the proximal thread 122 engaged proximally, furtheradvancing the implant causes the distal bone portion to move proximallyrelative to the implant faster than the proximal bone portion movesproximally and thus move the bone portions closer together.Alternatively, to move the bone portions further apart to distract thefracture, the distal thread pitch 128 may be made smaller than theproximal thread pitch 130 so that with the distal thread 112 engageddistally and the proximal thread 122 engaged proximally, furtheradvancing the implant causes the distal bone portion to move proximallyrelative to the implant more slowly than the proximal bone portion movesproximally and thus move the bone portions further apart. Preferably,the bone implant 100 has a through bore, or cannulation 101, coaxialwith the longitudinal axis 110 to permit the bone implant 100 to beinserted over a guide wire.

The bone implant 100 of FIGS. 1-4, may advantageously be provided in aset containing a plurality of threaded implants as shown in theillustrative example of FIGS. 5-7. For example, it is advantageous in asurgical procedure to minimize the number of steps and the amount oftime needed to complete the procedure. In a bone fixation procedure, asurgeon often makes an initial sizing decision based on medical imaging.During the procedure, it may become expedient to change thepredetermined size based on observation of the surgical site or the fitof trial implants or instruments. For example, a surgeon may determineinitially that a smaller threaded implant is appropriate. However,during preparation of the site, the surgeon may determine that a largerthreaded will better grip the bone or fill, for example, a canal in thebone. The illustrative set of implants shown in FIGS. 5-7 facilitateschanging between sizes. Each implant thread 140, 150, 160 in the set hasa minor diameter 142, 152, 162, a major diameter 144, 154, 164, and apitch 146, 156, 166. The minor diameters 142, 152, 162 are equal to oneanother so that a single diameter drill will provide an initial borehole appropriate for all the threads in the set. The pitches 146, 156,166 are equal to one another so that all of the threads in the set willthreadably engage a helical thread of the same pitch. The majordiameters 144, 154, 164 may increase to provide progressively more bonepurchase or, for example, to span increasing larger intramedullarycanals. For example, with the set of implants of the illustrativeexample of FIGS. 5-7, a surgeon may drill a hole equal to the minordiameters 142, 152, 162 and then tap the hole with a tap correspondingto the thread of the smallest major diameter thread 140. The tactilefeedback received by the surgeon as the tap is inserted will indicate tothe surgeon if the thread major diameter is sufficient to provide adesired level of bone engagement. For example, the surgeon can feel ifthe tap is engaging the cortical walls of an intramedullary canal or ifthe tap is in softer cancellous bone. If the surgeon determines thatgreater engagement is desired, the surgeon can next tap the hole with atap corresponding to the thread of the next larger major diameter thread150. Since the minor diameters 142, 152, 162 and thread pitches 146,156, 166 are the same for all of the impinats in the set, the next tapwill thread into the previously tapped hole and increase the bone threadmajor diameter without damaging the bone thread. Once the desired boneengagement is achieved, the surgeon may then insert the desired implant140, 150, 160. If in tapping the larger major diameter thread, thesurgeon determines that the bone is providing too much resistance, thesurgeon may revert to the smaller sized implant since the threads arestill compatible. Alternatively to using a separate tap, the screwthreads may be configured as self-tapping so that the implants may bethreaded directly into the bored hole.

In addition to the sizing advantages of having the same minor diameter142, 152, 162 across a family of implants, it is also advantageousbecause the distal threaded portion of each implant will have a similarbending stiffness to each of the other implants 140, 150, 160 since thecontinuous wall of the minor diameter contributes much more to thebending stiffness than the helical thread itself. This similar bendingstiffness means that they can be inserted around a similar bendingradius with a similar torque.

In the illustrative example of FIGS. 5-7, each implant 140, 150, 160 hasa mid-portion diameter 148, 158, 168 equal to the corresponding majordiameter 144, 154, 164. The increasing mid-portion diameters provideprogressively less flexible mid-portions across the set of implants and,for example, canal filling for increasingly larger bones if used in theintramedullary canal. If the implants incorporate the optionalincreasing mid-portion diameter as shown, then it is desirable tore-drill the mid-portion of the bone hole to accommodate the mid-portionwhen an increase in implant size is desired. However, the distal,threaded portion of the bone hole does not need to be re-drilled so theimplant threads will not be damaged by drilling. The mid-portiondiameter may also be larger than the corresponding distal thread majordiameter to further increase the mid-portion stiffness.

Alternatively to, or in addition to, the threaded distal portion 104 andmid-portion 106 having different sectional moduli, the threaded distalportion 104 and mid-portion 106 may have different material propertiessuch as two different materials or different conditions of the samematerial to produce a difference in bending stiffness between them.

In the illustrative example of FIGS. 36-41, an implant 170 has separatefirst and second members 172, 174 permanently joined together. The firstmember 172 includes an elongate body 176 with a proximal end 178, adistal end 180, a longitudinal axis 182, and an axial through bore 184.The proximal end 178 of the first member includes a pair of transversethrough bores 181, 183. Each transverse bore 181, 183 defines alongitudinal axis and the axes form an angle 185 between them about thelongitudinal axis 182 as best seen in FIG. 39. Providing more than onetransverse through bore increases options for attaching the implant tobone fragments and options for fixation direction. Both bores may beused for fixation or the one that is most conveniently located may beused. Preferably the angle 185 is in the range of 0 to 90 degrees. Morepreferably the angle 185 is in the range of 20 to 90 degrees. In theillustrative example of FIGS. 36-41, the angle 185 is 45 degrees. Theproximal end 178 also includes opposed flats 187 for engaging a driverin torque transmitting relationship. An internal thread 189 within thebore 184 is engageable with, e.g., a threaded draw bar to secure thefirst member to a driver.

The second member 174 includes an elongate body 186 with a proximal end188, a distal end 190, a longitudinal axis 192, an external helicalthread 194, and an axial through bore 196. The distal end 180 of thefirst member 172 and the proximal end 188 of the second member 174 mayhave complementary geometries to aid in joining them. In theillustrative example of FIGS. 36-41, the distal end 180 of the firstmember has a stepped conical taper and the proximal end 188 of thesecond member has a corresponding stepped conical socket 198. The matingsurfaces may be any suitable shape as determined by the materials andjoining technique including but not limited to plug and socket joints(as shown), scarf j oints, butt joints, dovetail joints, finger joints,and lap joints. The joint may be reinforced with a third component suchas an adhesive, pin, or key. The joint may be formed by mechanicalinterlock, chemical bonding, molding, welding or other suitable joiningprocess. The final assembled implant 170, has a distal portion 191, amid-portion 193 and a proximal portion 195 and may have the threadforms, diameters, and relationships as described relative to theexamples of FIGS. 1-7.

The first and second components 172, 174 may be made of differentmaterials or different conditions of the same material. For example,they may be made of polymers, metals, or ceramics. Metals may includestainless steel alloys, titanium, titanium alloys, cobalt-chromium steelalloys, nickel-titanium alloys, and/or others. Polymers may includenonresorbable polymers including polyolefins, polyesters, polyimides,polyamides, polyacrylates, poly(ketones), fluropolymers, siloxane basedpolymers, and/or others. Polymers may include resorbable polymersincluding polyesters (e.g. lactide and glycolide), polyanhydrides,poly(aminoacid) polymers (e.g. tyrosine based polymers), and/or others.Other possible materials include nonresorbable and resorbable ceramics(e.g. hydroxyapatite and calcium sulfate) or biocompatible glasses. Theymay be made of homogenous materials or reinforced materials. They may bemade of crystallographically different materials such as annealed versuscold worked. It is preferable for the mid portion 193 and proximalportion 195 to have a higher bending stiffness than the distal portion191 and the distal portion preferably has a bending stiffness low enoughfor it to be inserted along a curved path in bone.

In a first example, the first component may be made of a metal with arelatively high degree of cold work and the second component of a metalwith a relatively low amount of cold work such as for example annealedand cold worked stainless steel. The components may be joined forexample by welding. However, as discussed relative to Table 1, mostmetals are far too stiff to allow threading along a curved path in abone within suitable torsional loads.

Preferably the distal portion is made of a polymer. In a second example,the first component is made of a metal, such as stainless steel or atitanium alloy, and the second component is made of a polymer such aspolyetheretherketone (PEEK) or a polylactide polymer (e.g. PLLA). Thecomponents may be joined such as for example by threading them together.

Preferably both components are made of polymers. In a third example, thefirst and second components are both made of non-resorbable polymers.For example, the first component may be made of fiber reinforced PEEK(e.g. Invibio PEEK-Optima™ Ultra-Reinforced) and the second componentmay be made of neat (unreinforced) PEEK (e.g. Invibio PEEK-Optima™Natural). The fiber reinforced PEEK is strong while the neat PEEK isrelatively flexible allowing it to be easily threaded around a curvedpath even while having a relatively large bone filling diameter. Thecomponents may be joined, e.g. by molding the components as a continuousmatrix with first component fiber reinforcement and second componentneat polymer with polymer chains extending across the joint interface.In the example of FIGS. 36-41, the second component is relatively moretransparent to laser radiation than the first component and the partsare joined by laser welding at the conical interface. The laser energypasses relatively easily through the second component and is absorbed bythe first component so that localized heating at the conical interfacetakes place causing the polymer constituent of the two components tofuse together.

In a fourth example, the first and second components are made ofresorbable polymers. For example, the mid-portion may be made of a glassfiber reinforced PLLA (e.g. Corbion-Purac FiberLive™) and the distalportion may be made of neat PLLA.

Alternatively, the first member 172 and second member 174 may form onecontinuous part with different properties between first and secondportions. The difference in properties may be achieved, for example, bydifferent processing (e.g. thermal processing) or blending materials.For example, different polymers may be combined in a single injectionmold cavity and formed together. The polymers may be blended so thatthere is a transition between them. In another example, stiffeningand/or strengthening material, e.g. fibers, whiskers, and/or granules,may be selectively incorporated in, e.g., the first portion.

FIGS. 42 and 43 illustrate an example of an implant 270 similar to thatof FIGS. 36-41 except that the first member 272 is not cannulated, thefirst member 272 extends the full length of the second member 274, andthe transverse holes 281, 283 are coplanar. The implant 270 may beassembled as with the prior example including by using complimentaryscrew threads in the proximal region of the second member 274 and midportion of the first member 272 as indicated by reference number 250.The implant 270 of the example of FIGS. 42 and 43 may be include any ofthe materials and features described relative to the prior examples. If,for example, the first member 272 is made of a radiographically moreopaque material than the second member 274, then the first member willprovide a radiographic marker over the entire length of the screw 270that may be radiographically visualized during and after surgery toconfirm implant placement. For example, a metal first component andpolymer second component would provide for radiographic visualization ofthe metal first component. It has been found by the present inventorsthat the bending stiffness of the distal end of the implant is notmaterially changed by eliminating the axial through bore of the firstcomponent and is essentially unchanged when the bending stiffness of aguide wire is accounted for which was optionally used with the previouscannulated implant examples. The guide wire is not necessary inasmuch asthe implant 270 will follow a curved path receiving it. The transverseholes 181, 183 may be provided in any number or not at all as desiredbut it has been found that one is sufficient and two provides the userwith additional fixation choice.

FIGS. 44 and 45 illustrate a bone implant 400 useful for stabilizingbone fractures according to one example of the invention. The boneimplant 400 includes a body 402 defining a longitudinal axis 404extending between a proximal end 406 and a distal end 408. The body hasan elongate distal portion 410 having an outer surface 412 defining ascrew thread 414 having a minor diameter 416 and a major diameter 418.The body has an elongate proximal portion 430 having a non-threadedouter surface 432. Passages 434 and 436 are each formed through theproximal portion 430 transverse to the longitudinal axis from a firstopening 438, 440 on the surface of the proximal portion to a secondopening 442, 444 on the surface of the proximal portion. A driverengaging feature is formed at the proximal end for engaging a driver intorque transmitting relationship. The driver engaging feature may be amale feature or a female feature. Preferably it is a polygonal featureengageable with a correspondingly shaped driver. In the example of FIGS.44 and 45, the driver engaging feature is a hexagonal socket 446 formedin the proximal end of the implant. The socket 446 includes a threadedrecess 448 for threaded engagement with other tools such as a driverretaining draw rod, a cross pinning guide, or the like. The distalportion is responsive to rotation of the implant to thread into a boneand advance the bone implant into the bone. This rotary advancementaction is advantageous compared to typical bone nails that are impactedinto the bone since the threaded advancement is less stressful to thebone and surrounding tissues. As the distal portion is threaded into thebone, it pulls the proximal portion into the bone. The distal threadedportion is anchored in the bone by the thread 414. The smooth proximalportion may be positioned to span a fracture so that, for example, nosharp edges are engaged with the fracture and no stress concentratingfeatures that might weaken the implant span the fracture.

In the example of FIGS. 44 and 45, the proximal portion has a length 450measured from the free proximal end 406 to the proximal start 452 of thethreads of the distal portion. The proximal portion has a maximumdiameter. For example for a conical or cylindrical proximal portion themaximum diameter is simply the largest diameter along the proximalportion. For an ovoid proximal portion, the maximum diameter would bethe major diameter of the elliptical cross section. For other shapes,such as fluted proximal portions, the maximum diameter is the maximumdimension normal to the longitudinal axis 404 of the proximal portion.The maximum diameter is preferably constant over a portion of theproximal portion length to provide a uniform thickness for spanning afracture. For example, the maximum diameter is preferably uniform overat least one-fourth of the proximal portion length; more preferably atleast one-third; more preferably at least one-half; more preferably morethan one-half. In the illustrative example of FIGS. 44 and 45, theproximal portion has a constant cylindrical diameter over its entirelength. The driver engaging feature preferably has a maximum dimensionnormal to the longitudinal axis that is less than or equal to themaximum diameter of the proximal portion so that, for example, theproximal end of the bone implant may be seated below the bone surface.

The bone implant may be a unitary construct, like shown in theillustrative example of FIGS. 1-4, in which the proximal and distalportions are formed of one continuous material. Optionally, the proximaland distal portions may be separate components joined together as shownin the example of FIG. 36 and the example of FIG. 42. In theillustrative example of FIGS. 44 and 45, the bone implant includes asleeve 460 surrounding a separate core 462. The sleeve and core arejoined together to form the body. Various methods may be used to jointhe sleeve and core. For example, they may be threaded, pinned, bonded,welded, or otherwise joined. In the example of FIGS. 44 and 45, thesleeve is threaded onto the core via an internal thread 464 andcorresponding male thread 466 formed on the core. The sleeve is furtherpinned to the core with a pin 468 pressed through holes 470, 472 in thesleeve wall and in the core.

As described relative to previous examples, it is desirable for thedistal portion to have a lower bending resistance than the proximalportion. In one example, the sleeve is at least partially formed of apolymer and the core is at least partially formed of a metal. In theexample of FIGS. 44 and 45, the sleeve is machined from a polymer andincludes the distal screw thread while the core is machined from a metaland includes the proximal portion. In one example, the core is made of abiocompatible titanium alloy and the sleeve is made of a biocompatiblepoly(ketone) polymer such as, for example, polyetheretherketone. Inanother example, the core is made of a suitable biocompatible metal andthe sleeve is made of a resorbable polymer so that, over time, thesleeve will resorb in the patient's body and allow gradually increasingmotion of the bone and load transfer to the bone to promote healing. Thecore may extend partway toward the distal end as in the example of FIG.36, all the way to the distal end as in the example of FIG. 42, or itmay extend past the distal end as in the example of FIGS. 44 and 45.With the tip 480 of the core extending beyond the distal end, the tip480 provides an easier start of the implant into a hole in the bone and,as shown in the example of FIGS. 44 and 45, the tip 480 provides asmooth bearing surface for following a curved path in a bone.

FIGS. 46 through 49 illustrate a bone implant 500 similar to that ofFIGS. 44 and 45. The bone implant 500 includes a core 502 and a sleeve504. In the example of FIGS. 44 and 45, the smooth proximal portion 506is more evenly proportioned over the core and sleeve. Also, the coresteps up more gradually in diameter from the distal end 508 to theproximal end 510 resulting in a more gradual transition in bendingstiffness over three zones. In a first zone 512, a relatively thinportion of the core is surrounded by a relatively thick portion of thesleeve. In a second zone 514, a relatively thicker portion of the coreis surrounded by a relatively thinner portion of the sleeve. In a thirdzone 516, only a relatively thicker portion of the core remains. Also,in the example of FIGS. 46 through 49 a slip resisting feature isprovided on the core and a polymer sleeve is molded to the core so thatthe polymer and slip resisting feature interdigitate. The slip resistingfeature may be knurling, threads, grooves, splines, spikes, holes, orother features. The slip resisting feature may be oriented to enhancetorque transfer, longitudinal force transfer, or otherwise oriented. Inthe example of FIGS. 46 and 47, the slip resisting feature includeslongitudinal splines 518 to enhance the ability to transfer torquebetween the core and sleeve. Longitudinal force transfer is sufficientlyaccommodated by the bonding of the sleeve to the core during the moldingprocess.

In use, the preceding implants may be provided in an appropriate sizeand inserted into a bone to span a fracture in the bone. Preferably theproximal portion of the implant spans the fracture. The arrangement of asmooth proximal portion and a threaded distal portion permits rotatingthe bone implant to cause the threaded distal portion to engage the boneand pull the proximal portion of the bone implant into a positioningspanning the fracture. In the case of an implant comprising a resorbablepolymer, the polymer will resorb over time in the patient to graduallytransfer load to and permit motion of the bone to enhance healing of thefracture. One or more pins or screws may be inserted so that they extendthrough one or more of the passages in the proximal end and through aportion of the bone to fix the bone to the proximal portion of theimplant. For example with the distal end of the bone implant fixed byengagement of the distal threads in a distal portion of the bone aproximal portion of the bone may be secured with pins or screws asdescribed. This may be used to hold compression or distraction on boneportions on opposing sides of the fracture or to attach loose bonefragments.

FIGS. 50-53 illustrate a bone implant 600 similar to the precedingexamples inasmuch as it has a smooth rod-like proximal portion 602 and athreaded distal portion 604. The proximal portion 602 has one or moretransverse passages through the proximal portion, each passage extendingfrom a first opening on the surface of the proximal portion to a secondopening on the surface of the proximal portion. The distal portion maybe threaded into a bone to secure the implant 600 to the bone at thedistal end. The proximal portion, is preferably positioned to bridge afracture to provide support to the fracture while the fracture heals.The transverse passages can receive a fastener such as a pin, wire,screw or the like to connect the proximal portion to bone. In theillustrative example of FIGS. 50-53, the implant 600 is configured forplacement in the intramedullary canal of a fibular bone to support afracture of the fibular bone and optionally to support screws forreinforcing the syndesmosis joint of an ankle. The proximal portionincludes a first pair of holes 606 perpendicular to the implantlongitudinal axis 608 and angled relative to one another about the axis608. The first pair of holes 606 is positioned nearer the proximal end610 of the implant to receive fasteners for attaching the implant 600 toa portion of the bone, or fragment, proximal to a fracture. The implantfurther includes a second pair of holes 612 perpendicular to the implantlongitudinal axis and, in this example, parallel to one another. Thesecond pair of holes 612 is positioned distal to the first pair and isarranged to receive fasteners that extend through the fibula and intothe tibia to reinforce the syndesmosis joint. In the illustrativeexample of FIGS. 50-53 the implant 600 is a unitary construction. Inother embodiments, the implant 600 may include a greater or a lessernumber of transverse holes or no holes at all. The transverse holes maybe perpendicular to the axis 608 as shown or at any other angle suitablefor the target anatomy. The implant may be made of two or more partsjoined together as in the previous examples. The distal portion 604includes a distal thread 620 having a major diameter 622, a minordiameter 624, and a pitch 626.

The various examples according to the invention have a decreased bendingstiffness of the distal portion relative to the proximal portion usingvarious strategies including different section moduli and differentmaterials. It is desirable for the distal thread to have a lower bendingstiffness than conventional bone screws of a similar major diameter. Inthe illustrative examples, the bending stiffness of the distal portionmay be lowered by utilizing a novel screw thread. For example, a threadaccording to an example of the invention has a smaller minor diameterand/or a larger pitch than a conventional bone screw thread. Table 3compares illustrative examples of screw thread geometry according toexamples of the invention to the industry standard bone screw threadsdescribed in ASTM F543.

TABLE 3 Screw thread geometry - Dimensions in mm B C D E Maj. Maj. Min.Min. A dia. dia. dia. dia. F B/E C/D B/F C/F D/F E/F Thread max min maxmin Pitch ratio ratio ratio ratio ratio ratio ASTM HA 1.5 1.50 1.35 1.101.00 0.50 1.50 1.23 3.00 2.70 2.20 2.00 ASTM HA 2.0 2.00 1.85 1.30 1.200.60 1.67 1.42 3.33 3.08 2.17 2.00 ASTM HA 2.7 2.70 2.55 1.90 1.75 1.001.54 1.34 2.70 2.55 1.90 1.75 ASTM HA 3.5 3.50 3.35 2.40 2.25 1.25 1.561.40 2.80 2.68 1.92 1.80 ASTM HA 4.0 4.00 3.85 2.90 2.75 1.50 1.45 1.332.67 2.57 1.93 1.83 ASTM HA 4.5 4.50 4.35 3.00 2.85 1.75 1.58 1.45 2.572.49 1.71 1.63 ASTM HA 5.0 5.00 4.85 3.50 3.35 1.75 1.49 1.39 2.86 2.772.00 1.91 ASTM HB 4.0 4.00 3.85 1.90 1.75 1.75 2.29 2.03 2.29 2.20 1.091.00 ASTM HB 6.5 6.50 6.35 3.00 2.85 2.75 2.28 2.12 2.36 2.31 1.09 1.04ASTM HC 2.9 2.90 2.79 2.18 2.03 1.06 1.43 1.28 2.74 2.63 2.06 1.92 ASTMHC 3.5 3.53 3.43 2.64 2.51 1.27 1.41 1.30 2.78 2.70 2.08 1.98 ASTM HC3.9 3.91 3.78 2.92 2.77 1.27 1.41 1.29 3.08 2.98 2.30 2.18 ASTM HC 4.24.22 4.09 3.25 2.95 1.27 1.43 1.26 3.32 3.22 2.56 2.32 ASTM HD 4.0 4.033.97 2.95 2.89 1.59 1.39 1.35 2.53 2.50 1.86 1.82 ASTM HD 4.5 4.53 4.472.95 2.89 2.18 1.57 1.52 2.08 2.05 1.35 1.33 Example 1 3.55 3.45 2.051.95 2.75 1.82 1.68 1.29 1.25 0.75 0.71 Example 2 3.25 3.10 1.50 1.352.25 2.41 2.07 1.44 1.38 0.67 0.60 Example 3 5.25 5.10 3.00 2.85 2.751.84 1.70 1.91 1.85 1.09 1.04

Column A is a description of each of the threads being compared. ASTMType HA threads correspond to the standard for bone screws having aspherical undersurface head, a shallow asymmetrical buttress thread, anda deep screw head. ASTM Type HB threads correspond to the standard forbone screws having a spherical undersurface head, a deep asymmetricalbuttress thread, and a shallow screw head. ASTM Type HC threadscorrespond to the standard for bone screws having a conical undersurfacehead and a symmetrical thread. ASTM Type HD threads correspond to thestandard for bone screws having a conical undersurface head and anasymmetrical thread. Column B is the maximum major diameter for thethread including permitted manufacturing tolerances. Column C is theminimum major diameter for the thread including permitted manufacturingtolerances. Column D is the maximum minor diameter for the threadincluding permitted manufacturing tolerances. Column E is the minimumminor diameter for the thread including permitted manufacturingtolerances. Column F is the thread pitch. Column B/E is the ratio of themaximum major diameter to the minimum minor diameter and represents thelargest major diameter to minor diameter ratio for the thread. ColumnC/D is the ratio of the minimum major diameter to the maximum minordiameter and represents the smallest major diameter to minor diameterratio for the thread. Column B/F is the ratio of the maximum majordiameter to the pitch and represents the largest major diameter to pitchratio for the thread. Column C/F is the ratio of the minimum majordiameter to the pitch and represents the smallest major diameter topitch ratio for the thread. Column D/F is the ratio of the maximum minordiameter to pitch and represents the largest minor diameter to pitchratio for the thread. Column E/F is the ratio of the minimum minordiameter to pitch and represents the smallest minor diameter to pitchratio for the thread.

Referring to columns B/E and C/D, standard bone screws with a threadmajor diameter less than 4.0 mm have a major diameter to minor diameterratio less than 1.7.

Referring to column F of Table 3, standard bone screws with a threadmajor diameter less than 6.5 mm have a pitch less than 2.2 mm. Standardbone screws with a thread major diameter less than 4.5 mm have a pitchequal to or less than 1.75 mm. Standard bone screws with a thread majordiameter less than 4.0 mm have a pitch less than 1.5 mm. Looking at itanother way, referring to columns B/F and C/F, standard bone screws havea major diameter to pitch ratio greater than 2. Standard bone screwswith a thread major diameter less than 4.0 mm have a major diameter topitch ratio greater than 2.5. Referring to columns D/F and E/F, standardbone screws have a minor diameter to pitch ratio greater than or equalto 1. Standard bone screws with a thread major diameter less than 4.0 mmhave a minor diameter to pitch ratio greater than or equal to 1.75.

Examples of the invention have a thread with a smaller minor diameterand/or a larger pitch than standard bone screws of a similar size to,for example, enable the screw thread to bend to follow a curved path ina bone.

Referring to Example 1 according to the invention, the example threadhas a 3.5 mm nominal major diameter, a 2.00 mm nominal minor diameter, apitch of 2.75 mm, a major diameter to minor diameter ratio between 1.68and 1.82, a major diameter to pitch ratio between 1.25 and 1.29, and aminor diameter to pitch ratio between 0.71 and 0.75. Comparing Example 1to ASTM HA 3.5 and ASTM HC 3.5, it is seen that the thread of Example 1has a minor diameter approximately 15-20% smaller than similar sizedstandard bone screws. In addition, the thread of Example 1 has a pitchmore than double the length of similar sized standard bone screws. Themajor diameter to minor diameter ratio for the thread of Example 1 isapproximately 20-30% greater than for similar sized bone screws. Themajor diameter to pitch ratio for the thread of Example 1 is less than50% that of similarly sized standard screws and the minor diameter topitch ratio for the thread of Example 1 is less than 40% that ofsimilarly sized standard bone screws. With its unconventional decreasedminor diameter and increased thread pitch, a thread according to Example1 made of Ti-6A1-4V has been shown by the present inventors to be ableto bend to follow the natural curve of the intramedullary canal of ahuman fibula.

Referring to Example 2 according to the invention, the example threadhas a 3.18 mm nominal major diameter, a 1.43 mm nominal minor diameter,a pitch of 2.25 mm, a major diameter to minor diameter ratio between2.07 and 2.41, a major diameter to pitch ratio between 1.38 and 1.44,and a minor diameter to pitch ratio between 0.60 and 0.67. Comparingexample 2 to ASTM HA 3.5 and ASTM HC 2.9, the most similar sizedstandard bone screw threads, it is seen that the thread of Example 2 hasa minor diameter approximately 30-40% smaller than similar sizedstandard bone screws. In fact, the thread of Example 2 has a minordiameter smaller than an ASTM HA 2.7 thread and most closely resemblesthat of the much smaller ASTM HA 2.0 thread. In addition, the thread ofExample 2 has a pitch more than double that of similar sized standardbone screws. The major diameter to minor diameter ratio for the threadof Example 2 is approximately 50-65% greater than for similar sized bonescrews. The major diameter to pitch ratio for the thread of Example 2 isapproximately 50% that of similarly sized standard screws and the minordiameter to pitch ratio for the thread of Example 2 is less than 35%that of similarly sized standard bone screws. With its unconventionaldecreased minor diameter and increased thread pitch, a thread accordingto Example 2 made of polyetheretherketone has been shown by the presentinventors to be able to bend to follow the natural curve of theintramedullary canal of a human clavicle.

Referring to Example 3 according to the invention, the example threadhas a 5.18 mm nominal major diameter, a 2.93 mm nominal minor diameter,a pitch of 2.75 mm, a major diameter to minor diameter ratio between1.70 and 1.84, a major diameter to pitch ratio between 1.85 and 1.91,and a minor diameter to pitch ratio between 1.04 and 1.09. Comparingexample 3 to ASTM HA 5.0, the most similar sized standard bone screwthread, it is seen that the thread of Example 3 has a minor diameterapproximately 15% smaller than similar sized standard bone screws. Inaddition, the thread of Example 3 has a pitch approximately 60% greaterthan similar sized standard bone screws. The major diameter to minordiameter ratio for the thread of Example 3 is approximately 23% greaterthan for similar sized bone screws. The major diameter to pitch ratiofor the thread of Example 3 is approximately 67% that of similarly sizedstandard screws and the minor diameter to pitch ratio for the thread ofExample 3 is less than 55% that of similarly sized standard bone screws.With its unconventional decreased minor diameter and increased threadpitch, a thread according to Example 3 made of polyetheretherketone hasbeen shown by the present inventors to be able to bend to follow thenatural curve of the intramedullary canal of a human clavicle.

Examples of threads according to the invention preferably have a pitchgreater than that for standard bone screws of a similar major diameter.For example, for threads with a major diameter less than 6.25 mm, it ispreferable to have a pitch greater than 2.2 mm; more preferably greaterthan 2.5; more preferably greater than or equal to 2.75. For threadswith a major diameter less than 4.0 mm, it is preferable to have a pitchgreater than 1.5 mm; more preferably greater than 1.75; more preferablygreater than 2.0; more preferably greater than 2.25; more preferablygreater than or equal to 2.75.

Examples of threads according to the invention having a major diameterless than 4.0 mm preferably have a major diameter to minor diameterratio greater than 1.7; more preferably greater than 1.8; morepreferably greater than 1.9; more preferably greater than 2.0.

Examples of threads according to the invention preferably have a majordiameter to pitch ratio less than 2; more preferably less than 1.75;more preferably less than 1.5; more preferably less than 1.4; morepreferably less than 1.3. For threads having a major diameter less than4.0 mm, the major diameter to pitch ratio is preferably less than 2.7;more preferably less than 2.5; more preferably less than 2.25.

Examples of threads according to the invention preferably have a minordiameter to pitch ratio less than 1.2; more preferably less than 1.0;more preferably less than 0.8; more preferably less than or equal to0.75, more preferably less than 0.7.

FIGS. 8-10 illustrate an implant being inserted into first and secondbone portions 200, 202 having a bone interface 204 between them. Theimplant could be any of the examples of FIGS. 1, 36, 42, 44, 46 and 50and the variations described herein. In the particular example of FIGS.8-10, the example of FIG. 1 is shown. A first or proximal bore 206 isformed in the first bone portion 200, across the bone interface 204, andinto the second bone portion 202. A second or distal bore 208 extendsdistally from the proximal bore 206 defining a curved path 210. Thescrew 100 is advanced through the proximal bore 206 until the distalscrew threads engage the distal bore 208 as shown in FIG. 9. Furtheradvancing the screw 100 causes it to bend to follow the curved path 210as shown in FIG. 10. Having a straight portion of the path, and thus thestraight mid portion of the screw 100, spanning the bone interfaceresults in a zero stress and strain state at the bone interface whichprevents separation of the bone portions 200, 202 at the interface 204.

FIGS. 11-35 depict an illustrative method of using an implant to fix afractured clavicle. The implant could be any of the examples of FIGS. 1,36, 42, 44, 46 and 50 and the variations described herein. In theparticular example of FIGS. 11-35, the example of FIG. 1 is shown. Apatient is placed in a beach chair position with the head rotated awayfrom the operative side. A bolster is placed between the shoulder bladesand head allowing the injured shoulder girdle to retract posteriorly. AC-arm is positioned to enable anterior-posterior (AP) and cephalic viewsof the operative site. A 2-3 cm incision 300 is made at the fracturesite along Langer's Lines running perpendicular to the long axis of theclavicle to expose the fracture site (FIG. 11). The platysma muscle isfreed from the skin and split between its fibers. The middle branch ofthe supraclavicular nerve is identified and retracted.

The medial end 302 of the lateral fragment 304 of the fractured clavicleis elevated from the fracture site incision (FIG. 12).

A K-wire 306, e.g. a 1.4 mm K-wire, is drilled into the canal of thelateral fragment 304 and advanced through the dorsolateral cortex 308and out through the skin (FIG. 13).

A wire driver is attached to the lateral portion of the K-wire and usedto back the wire out until it is lateral to the fracture 310 (FIG. 14).Bone clamps are used at the incision site to reduce the fracture andclamp the bone fragments in position. Proper reduction is confirmed withAP and cephalic radiographic views.

The K-wire 306 is advanced until it is preferably at least 20 mm medialto the fracture (FIG. 15).

A first dilator 312, e.g. a 3.2 mm dilator, is placed over the K-wireand advanced until it contacts the bone (FIGS. 16-17).

A second dilator 314, e.g. a 4.5 mm dilator, is placed over the firstdilator 312 and advanced until it contacts the bone (FIG. 18).

A drill guide 316 is placed over the second dilator 314 and advanceduntil it contacts the bone (FIG. 19).

The first dilator 312 is removed and a first lateral drill 318,corresponding to the minor diameter of the distal screw threads, e.g. a3.2 mm drill, is advanced over the K-wire into the bone, preferably atleast 20 mm medial to the fracture. A drill depth mark readable adjacentthe drill guide may be noted as a reference for implant sizing (FIG.20).

The K-wire is removed and replaced with a flexible guide wire 320, e.g.a nitinol guide wire, sized to fit within the screw cannulation, e.g. a1.4 mm guide wire. The flexible guide wire 320 is advanced through thefirst lateral drill and further along the intramedullary canal of themedial bone fragment and will curve to follow the intramedullary canalto define a curved path in the bone. Preferably, the guide wire isadvanced approximately 30 mm medial to the tip of the first lateraldrill 318 (FIG. 21).

The first lateral drill 318 is removed and a flexible shaft reamer 322,corresponding to the minor diameter of the distal screw threads, isguided over the flexible guide wire 320 to ream the medial portion ofthe curved path (FIG. 22) The flexible reamer 322 and second dilator 314are then removed.

A second lateral drill 324, having a diameter corresponding to thediameter of the mid-portion of the screw, e.g. a 4.5 mm drill, is guidedover the flexible guide wire to enlarge the bone hole laterally toreceive the mid-portion and proximal portion of the screw 100. Thesecond lateral drill 324 is advanced the same distance as the firstlateral drill (FIG. 23). The drilling step may be monitored in A/P andcephalic views with the C-arm to avoid perforating the bone cortex asthe second lateral drill 324 is advanced into the medial bone fragment326.

A flexible tap 328, having cutting threads corresponding to the distalthreads of the screw 100 is guided over the flexible guide wire to cutthreads into the medial bone fragment along the curved path (FIG. 24).The tap may serve as a trial implant and provides tactile feedbackregarding the fit of the implant in the bone. If it is determined that alarger screw is desirable, subsequent larger second drills may be usedto re-drill the lateral straight portion and subsequent larger flexibletaps may be used to increase the distal thread major diameter withouthaving to re-ream the medial curved portion of the bone hole. Once adesired level of thread purchase and canal filling are achieved, a depthmark readable adjacent the drill guide may be noted as a reference forthe required implant length. If a screw 100 with a proximal threadedportion is used, a lateral tap may be used to tap the lateral bonefragment to receive the proximal threads.

The screw 100 is attached to an inserter 330 and guided over theflexible guide wire until it is fully seated in the prepared threads inthe medial bone fragment (FIGS. 25 and 26). Optionally, the screw 100may be axially driven with a mallet through the lateral bone fragmentuntil just short of the distal thread engagement. The screw 100 may thenbe threaded into full engagement with the prepared threads in the medialfragment. Radiographic visualization may be used to ensure that thefracture is fully reduced and anatomically aligned in length androtation.

If a proximally threaded screw has not been used, or if additionalfixation is otherwise desired, cross fixation may be used. For example,a cross fixation guide 340 may be engaged with the implant inserter 330(FIG. 27). The cross fixation guide may include a knob 342 thatthreadingly engages the implant inserter 330 and a cross fixation guidesleeve 344 that abuts the lateral bone fragment adjacent the bone holeentrance. Rotating the knob 342 moves the cross fixation guide sleeve344 and implant inserter 330 axially relative to one another. With thecross fixation guide sleeve 344 abutting the lateral bone fragment 304,the implant inserter, implant, and medial bone fragment 326 will bedrawn laterally and the lateral bone fragment 304 will be pressedmedially to apply compression across the fracture.

Inner and outer drill sleeves 346, 348 are advanced through the guide340 until they abut the bone (FIG. 28). In the case of a screw such asthe examples of FIGS. 36, 42, 44, 46 and 50 having one or more preformedtransverse bores, the cross fixation guide may have one or moretargeting holes positioned to align with the one or more transversebores. In the case of a screw such as the example of FIG. 1 not havingpreformed transverse bores, cross fixation may be inserted directlythrough the screw 100 forming a transverse bore intraoperatively.

For example, a cross fixation wire 350 may be guided through the drillsleeves, through the near cortex, through the mid or proximal portionsof the screw, and into the far cortex of the lateral bone fragment (FIG.29). If wire cross fixation is adequate, the cross fixation guide may beremoved and the wire may be trimmed flush with the bone surface.

However, if screw cross fixation is desired, a screw depth gauge 352 maybe placed over the cross fixation wire to measure the projecting portionof the guide wire to determine the required screw length for bi-corticalfixation (FIG. 30).

A countersink tool 354 may be used to create a countersink for a crossfixation bone screw 356 (FIG. 31).

The appropriate length cross fixation screw 356 may then be guided overthe cross fixation wire 350 and seated into the bone (FIG. 32). Thesesteps may be repeated to place additional screws if desired.

FIGS. 33 and 34 illustrate the location of the screw 100 and crossfixation screws 356 relative to the lateral and medial bone fragments.

FIG. 35 illustrates the cross fixation screws 356 in the screw 100without the bone to obscure the view. Preferably the screw 100 is madeof a relatively soft material, e.g. a polymer, that facilitatesarbitrary placement of the cross fixation screws at any desiredlocation.

FIG. 54 illustrates a repair utilizing an implant according to oneexample of the invention. In the example of FIG. 54, the implant 600 ofFIGS. 50-53 is used to repair a fibula 700 having a distal fracture 702and fragment 704. The implant 600 is inserted through the distal end 706of the fragment 704 into the intramedullary canal of the fibula. As theimplant is rotated, the distal threaded portion engages the bone andpulls the proximal portion into the bone to a position bridging thefracture 702. The distal threaded portion bends to follow the curvedpath of the intramedullary canal. Bone screws 710 are placed into thefragment and the first pair of holes 606 of the implant 600 to securethe fragment. Additional screws 712 are placed into the fibula, thesecond pair of holes 612, and the tibia 714 to reinforce the syndesmosisjoint between the fibula and tibia.

FIG. 55 illustrates a repair utilizing an implant according to oneexample of the invention. In the example of FIG. 54, the implant 170 ofFIGS. 36-41 is used to repair an olecranon fracture of an ulna 720having a fracture 722 and a fragment 724. The implant 170 is insertedthrough the fragment 724 into the intramedullary canal of the ulna 720.As the implant is rotated, the distal threaded portion engages the boneand pulls the proximal portion into the bone to a position bridging thefracture 722. The distal threaded portion bends to follow the curvedpath of the intramedullary canal. Bone screws are placed into thefragment and the holes of the implant 170 to secure the fragment.

FIG. 56 illustrates a repair utilizing an implant according to oneexample of the invention. In the example of FIG. 55, the implant 170 ofFIGS. 36-41 is used to repair a Jone's fracture of a fifth metatarsal740 having a fracture 742 and a fragment 744. The implant 170 isinserted through the fragment 744 into the intramedullary canal of theulna 720. As the implant is rotated, the distal threaded portion engagesthe bone and pulls the proximal portion into the bone to a positionbridging the fracture 742. The distal threaded portion bends to followthe curved path of the intramedullary canal. Bone screws are placed intothe fragment and the holes of the implant 170 to secure the fragment.

Various examples have been presented to aid in illustrating theinvention. These various examples are illustrative but not comprehensiveand variations may be made within the scope of the invention. Forexample, the various features described relative to each example may beinterchanged among the examples.

What is claimed is:
 1. A bone implant comprising an elongate body havinga distal portion and a proximal portion spaced longitudinally relativeto a longitudinal axis, the distal portion having a helical distalthread formed thereon, the distal thread having a major diameter, aminor diameter, and a pitch, the distal thread being operable to bend asit is threaded into a bone to follow a curved path, the distal threadhaving a bending stiffness and the proximal portion having a bendingstiffness, the bending stiffness of the proximal portion being greaterthan the bending stiffness of the distal thread.
 2. The bone implant ofclaim 1 wherein the ratio of the mid-shaft portion bending stiffness tothe distal portion bending stiffness is in the range of 2:1 to 20:1. 3.The bone implant of claim 1 wherein the torque required to turn thedistal thread into a bone to follow a threaded curved path having aradius of curvature of 50 mm is less than 5 inch-lbs.
 4. The boneimplant of claim 1 wherein the proximal portion of the body has anon-threaded outer surface having a diameter, the diameter of theproximal portion being greater than or equal to the major diameter ofthe distal thread.
 5. The bone implant of claim 1 further comprising apassage formed through the proximal portion transverse to thelongitudinal axis from a first opening on the surface of the proximalportion to a second opening on the surface of the proximal portion. 6.The bone implant of claim 1 wherein the proximal portion has a lengthmeasured from a free end to a proximal start of the distal thread, theproximal portion having a maximum diameter, the maximum diameter beinguniform over at least one-fourth of the proximal portion length.
 7. Thebone implant of claim 6 further comprising a driver engaging featureformed at the proximal end for engaging a driver in torque transmittingrelationship, the driver engaging feature having a maximum dimensionnormal to the longitudinal axis that is less than or equal to themaximum diameter.
 8. The bone implant of claim 1 further comprising ahelical proximal thread formed on the proximal portion.
 9. The boneimplant of claim 8 further comprising a mid-portion between the distalthread and the proximal thread, wherein the proximal thread has a majordiameter and a minor diameter, the proximal thread minor diameter beingequal to the mid-portion outer diameter and the mid-portion diameter isgreater than or equal to the distal thread major diameter.
 10. The boneimplant of claim 1 wherein the proximal portion and the distal portioncomprise different materials.
 11. The bone implant of claim 10 whereinthe distal thread comprises a polymer.
 12. The bone implant of claim 11wherein the proximal portion comprises a metal.
 13. The bone implant ofclaim 11 wherein the distal thread comprises a resorbable polymer. 14.The bone implant of claim 11 wherein the proximal portion comprises areinforced polymer.
 15. The bone implant of claim 1 wherein majordiameter is less than 4.0 mm and the ratio of the major diameter to theminor diameter is greater than 1.7.
 16. The bone implant of claim 1wherein major diameter is less than 4.0 mm and the ratio of the majordiameter to the minor diameter is greater than 2.0.
 17. The bone implantof claim 1 wherein the ratio of the major diameter to the pitch is lessthan 2.0.
 18. The bone implant of claim 1 wherein the ratio of the majordiameter to the pitch is less than 1.5.
 19. The bone implant of claim 1wherein the ratio of the minor diameter to the pitch is less than 1.0.The bone implant of claim 1 wherein the ratio of the minor diameter tothe pitch is less than or equal to 0.75.